The overall objectives are an analysis of the factors controlling the cessation of cell growth under conditions of high cell density and the resumption of growth when conditions of low cell density are restored. A sensitive parameter of cellular growth is ribosomal RNA (rRNA) synthesis and particular emphasis is therefore placed on ascertaining that may be closely related to both the onset and the decline of rRNA synthesis during the growth cycle. We are also analyzing the details of a rapid initial increase in the capacity for protein synthesis that occurs upon dilution to low density. This process is undoubtedly a biochemical prerequisite for the subsequent onset of rRNA synthesis and we are attempting to define the process in terms of the mRNA utilized and the protein products that are synthesized. We further propose to analyze the regulation of this increased protein synthetic capacity in terms of the levels of initiator tRNA and of protein chain initiating activity.